The goal of this project is to identify the brain areas that mediate effects of sex hormones on ultrasonic communication by female golden hamsters. Areas selected for initial study (a) concentrate radioactively labeled estradiol from the general circulation, and (b) have been implicated in the control of female receptive behaviors by previous studies using lesion or hormone-implant techniques. In addition, several of these brain sites have been shown to exert at least partial control over vocal communication in other species. In its initial phase, this project will use lesion techniques to identify candidate areas for the mediation of hormonal effects. Local implants of estradiol then will specify regions where hormonal stimulation is sufficient to stimulate or depress ultrasound production. Finally, implants of estrogen-blocking agents will indicate areas that are essential, or necessary, for the mediation of estradiol effects on female ultrasonic communication. These results will increase our understanding of the neuroendocrine mechanisms controlling biologically important social communications in animals.